EL7556BC Elantec Semiconductor, EL7556BC Datasheet - Page 12

• Manufacturer Part Number: EL7556BC
• Description: Integrated Adjustable 6 Amp Synchronous Switcher
• Manufacturer: Elantec Semiconductor

EL7556BC
Integrated Adjustable 6 Amp Synchronous Switcher
exceeds the thermal trip-point, the OT pin will output a
logic 0. The upper and lower trip points are set to 135 ºC
and 100ºC respectively. To enable thermal shutdown
this pin should be tied directly to OUTEN. Use of this
feature is recommended during normal operation
Power Good and Power On Reset
During power up the output regulator will be disabled
until VIN reaches a value of approximately 4.0V.
Approximately 500mV of hysteresis is present to elimi-
nate noise induced oscillations.
Under-voltage and over-voltage conditions on the regu-
lator output are detected through an internal window
comparator. A logic 1 on the PWRGD output indicates
that regulated output voltage is within ±10% of the nom-
inally programmed output voltage. Although small, the
typical values of the PWRGD threshold will vary with
changes to external feedback (and resultant loop gain) of
the system. This dependence is shown in the typical per-
formance curves.
Thermal Management
The EL7556BC utilizes “fused lead” packaging technol-
ogy in conjunction with the system board layout to
achieve a lower thermal resistance than typically found
in standard 28-pin SO packages. By fusing (or connect-
ing) multiple external leads to the die substrate within
the package, a very conductive heat path to the outside
of the package is created. This conductive heat path
MUST then be connected to a heat sinking area on the
PCB in order to dissipate heat out and away from the
device. The conductive paths for the EL7556BC pack-
age are the fused leads: # 7, 9, 10, 11, 12, 18, and 19. If
a sufficient amount of PCB metal area is connected to
the fused package leads, a junction-to-ambient thermal
resistance of approximately 31°C/W can be achieved
(compared to 78°C/W for a standard SO28 package).
The general relationship between PCB heat-sinking
metal area and the thermal resistance for this package is
shown in the Performance Curves section of this data
sheet. It can be readily seen that the thermal resistance
for this package approaches an asymptotic value of
approximately 31°C/W without any airflow. Additional
information can be found in Application Note #8 (Mea-
suring the Thermal Resistance of Power Surface-Mount
Packages).
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If the thermal shutdown pin is connected to OUTEN the
IC will enter thermal shutdown when the maximum
junction temperature is reached. For a thermal shutdown
of 135ºC and power dissipation of 2.2W the ambient
temperature is limited to a maximum value of 67ºC (typ-
ical). The ambient temperature range can be extended
with the application of air flow. For example, the addi-
tion of 100LFM reduces the thermal resistance by
approximately 15% and can extend the operating ambi-
ent to 77ºC (typical). Since the thermal performance of
the IC is heavily dependent on the board layout, the sys-
tem designer should exercise care during the design
phase to ensure that the IC will operate under the worst-
case environmental conditions.